The invention relates to a toothbrush with a brush head and with plastic bristles and to a method for the manufacture of a plastic bristle for such a toothbrush.
In the case of toothbrushes either manually or electrically operated, the bristles conventionally comprise extruded monofilaments with a circular cross-section. Other cross-sections have already been proposed. The cleaning action of such toothbrushes, as well as a desired massaging action of the gums, takes place almost exclusively through the bristle ends which are rounded to avoid gum recession and injury. To this extent the bristle end has to fulfill two opposing requirements, namely on the one hand exerting an adequate brushing action on the tooth and on the other bringing about a restrained massaging of the gums. The cleaning of the tooth surfaces and gaps between the teeth which is vital is consequently inadequate due to the compromises made.
Numerous attempts have been made to incorporate the circumferential surface of the bristle by profiling into the brushing process and consequently increases the cleaning action. Thus, it is known (DE 31 16 189) to provide the bristle with different, spaced thickenings, which form further brushing edges. It is scarcely possible to rationally manufacture such a brush, if it is borne in mind that bristles are conventionally produced by spinning or extruding. Admittedly it is theoretically possible to bring about cross-sectional changes in the extrusion direction enabling such a bristle to be produced by extrusion. The monofilaments produced by extrusion must be subsequently finished and namely stretched and heat stabilized, to give the bristle the desired bendability and the necessary re-righting capacity. Such stretching in the case of injection moulded or extruded bristles with spaced thickenings would only lead to the bristle being stretched and constricted in the vicinity of the narrowest cross-sections between the thickenings, whereas the latter would be uninfluenced. Such a bristle would be completely unusable. Even if it proved possible to provide such a bristle with the necessary characteristics, the danger would exist of the bristle with the thickenings jamming in the interdental spaces and on pulling either tearing off or tearing out at the bristle head or injuring the gums in the interdental space, where they are particularly endangered due to inadequate dental neck adhesion.
In other toothbrush constructions (JP 03 289 906 A, JP 56-116 124 U, JP 60-145 828 U, JP 03-87332 U) either several monofilaments are twisted together or the individual monofilaments, which are themselves profiled, e.g. have a square cross-section (JP 03-289 906 A, JP 57-116 124 U), are profiled by helical twisting of the monofilament axis. This bristle has a better cleaning action as a result of its three-dimensionally twisted, sharp edges. The profile of this bristle is not suitable for dental care as a result of the numerous narrow turns and the resulting plurality of edges, which ineffectively slide over and beyond the comparatively smooth surface, but can injure the gums. The plurality of turns leads to large number of bending-weak points, which can impair the re-righting capacity of the bristle. The molecular structure of the monofilament is also impaired by the strong twisting. Such a bristle also easily become hooked in the interdental spaces.